From the Vascular Biology Program and Department of Surgery, Boston Children's Hospital (M.L.B., Y.D., K.S., K.Z., A.W., H.W., Y.L., S.W., L.Y., J.B., H.C.), Harvard Medical School, MA.
Department of Biochemistry and Molecular Biology, University of Oklahoma Health Sciences Center (M.L.B.).
Circ Res. 2019 Feb 15;124(4):e6-e19. doi: 10.1161/CIRCRESAHA.118.313028.
Atherosclerosis is, in part, caused by immune and inflammatory cell infiltration into the vascular wall, leading to enhanced inflammation and lipid accumulation in the aortic endothelium. Understanding the molecular mechanisms underlying this disease is critical for the development of new therapies. Our recent studies demonstrate that epsins, a family of ubiquitin-binding endocytic adaptors, are critical regulators of atherogenicity. Given the fundamental contribution lesion macrophages make to fuel atherosclerosis, whether and how myeloid-specific epsins promote atherogenesis is an open and significant question.
We will determine the role of myeloid-specific epsins in regulating lesion macrophage function during atherosclerosis.
We engineered myeloid cell-specific epsins double knockout mice (LysM-DKO) on an ApoE background. On Western diet, these mice exhibited marked decrease in atherosclerotic lesion formation, diminished immune and inflammatory cell content in aortas, and reduced necrotic core content but increased smooth muscle cell content in aortic root sections. Epsins deficiency hindered foam cell formation and suppressed proinflammatory macrophage phenotype but increased efferocytosis and anti-inflammatory macrophage phenotype in primary macrophages. Mechanistically, we show that epsin loss specifically increased total and surface levels of LRP-1 (LDLR [low-density lipoprotein receptor]-related protein 1), an efferocytosis receptor with antiatherosclerotic properties. We further show that epsin and LRP-1 interact via epsin's ubiquitin-interacting motif domain. ox-LDL (oxidized LDL) treatment increased LRP-1 ubiquitination, subsequent binding to epsin, and its internalization from the cell surface, suggesting that epsins promote the ubiquitin-dependent internalization and downregulation of LRP-1. Crossing ApoE/LysM-DKO mice onto an LRP-1 heterozygous background restored, in part, atherosclerosis, suggesting that epsin-mediated LRP-1 downregulation in macrophages plays a pivotal role in propelling atherogenesis.
Myeloid epsins promote atherogenesis by facilitating proinflammatory macrophage recruitment and inhibiting efferocytosis in part by downregulating LRP-1, implicating that targeting epsins in macrophages may serve as a novel therapeutic strategy to treat atherosclerosis.
动脉粥样硬化部分是由免疫和炎症细胞浸润血管壁引起的，导致主动脉内皮炎症和脂质堆积增强。了解这种疾病的分子机制对于开发新的治疗方法至关重要。我们最近的研究表明，衔接蛋白家族 epsin 是动脉粥样硬化形成的关键调节因子。鉴于病变巨噬细胞对动脉粥样硬化形成的重要贡献，髓系特异性 epsin 是否以及如何促进动脉粥样硬化形成是一个悬而未决的重要问题。
我们将确定髓系特异性 epsin 在调节动脉粥样硬化过程中病变巨噬细胞功能中的作用。
我们构建了载脂蛋白 E 背景下髓系细胞特异性 epsin 双敲除（LysM-DKO）小鼠。在西方饮食喂养下，这些小鼠的动脉粥样硬化病变形成明显减少，主动脉中的免疫和炎症细胞含量减少，主动脉根部的坏死核心含量减少，而平滑肌细胞含量增加。Epsin 缺失抑制泡沫细胞形成并抑制促炎型巨噬细胞表型，但增加原代巨噬细胞的吞噬作用和抗炎型巨噬细胞表型。在机制上，我们发现 epsin 缺失特异性增加了 LDLR（低密度脂蛋白受体）相关蛋白 1（LRP-1）的总蛋白和表面蛋白水平，LRP-1 是一种具有抗动脉粥样硬化特性的吞噬作用受体。我们进一步发现 epsin 通过 epsin 的泛素相互作用基序结构域与 LRP-1 相互作用。氧化型 LDL（ox-LDL）处理增加了 LRP-1 的泛素化，随后与 epsin 结合，并从细胞表面内化，表明 epsin 促进 LRP-1 的泛素依赖性内化和下调。将 ApoE/LysM-DKO 小鼠杂交到 LRP-1 杂合子背景上部分恢复了动脉粥样硬化，表明巨噬细胞中 epsin 介导的 LRP-1 下调在促进动脉粥样硬化形成中起关键作用。
髓系 epsin 通过促进促炎型巨噬细胞募集并通过下调 LRP-1 抑制吞噬作用来促进动脉粥样硬化形成，这表明靶向巨噬细胞中的 epsin 可能是治疗动脉粥样硬化的一种新的治疗策略。
